A current conventional under car measurement system for collision repair, such as the Blackhawk Shark system, has been in the marketplace for many years. It can monitor the locations of up to 12 under car measurement points with adequate accuracy and repeatability for collision repair. The system consists of a console, a long measuring beam housing 48 microphones, a set of proprietary adaptors, and up to 12 wired probes for attachment to vehicle body and frame points to be measured.
The probes are attached to the points of interests on the vehicle via combinations of adaptors. Each probe has two spark discharging point sources that can emit acoustic energy. The measuring beam, which is 3.6 meters in length, houses 48 microphones at calibrated positions that are tuned in monitoring acoustic energy at a preset ultrasonic frequency, placed longitudinally underneath the vehicle. The beam activates specific probes to emit acoustic energy, and when the acoustic energy reaches the microphone network, it logs the time of flight of the energy. The data is then sent to the console PC for processing, using an algorithm to determine the 3 dimensional location of each spark point source. Knowing the distance between the spark point sources and the dimensions of the adaptors employed, the system can extrapolate the three dimensional location of the point of interest at which the probe is attached. Four probes are assigned to undamaged points on the vehicle to set up the universal coordinate system that is used in recording all measured points. The XYZ coordinates of the measured point are then compared with the data of such points under the factory conditions in the database. The absolute values and XYZ deviations are then presented in the Graphic User Interface for a technicians' review. The console provides accommodation for adaptors, the monitor, PC, the printer, and probes. The application software and vehicle database is loaded in the PC.
In such conventional systems, the acoustic energy is produced by creating a high voltage spark between two electrodes on the probe. This energy is embodied as a single short, 50 uS pulse of acoustic energy composed of a wide band of sound frequencies. The acoustic energy travels at the speed of sound, or approximately 344 m/sec at sea level. The time of flight is the measure of the time interval for the acoustic energy to propagate in the air between the probe and a microphone positioned on the plane of the beam. The time of flight measured by each microphone is directly related to the straight line distance between the energy source (spark) and the microphone.
The measurement beam embeds 48 microphones, 24 each on opposing sides. The system uses at least six microphones for calculation of the speed of acoustic energy and the position or three dimensional coordinates of the source of the energy. The calculation of the sound speed is based on three microphones that are located in a straight line and at known positions relative to each other.
Assuming that three microphones (M1, M2 and M3), shown in FIG. 1A, are at equal distances (a) one from another and in a straight line and an energy source at position (S), the times of flight for energy to travel from S to each microphone are t1, t2 and t3 at a velocity of v.
The normal distance (x) from the beam to the source (S) can be defined in terms of each microphone by the following set of equations:x=sqrt[d12−(2*a−y)2]  (1)x=sqrt(d22−(a−y)2)  (2)x=sqrt(d32−y2)  (3)
Furthermore the distance from the source S to each microphone can be defined in terms of the measured time of flight to each microphone;d1=v*t1  (4)d2=v*t2  (5)d3=v*t3  (6)
Substituting for d in equations 1, 2 and 3 and then solving for v, we arrive at the following:v=sqrt[2*a2/(t12−2*t22+t32)]  (7)
Using v and the three measured times of flight, we can now solve for each distance in equations 4, 5 and 6.
To calculate the position of the source S(x,y,z), as illustrated in FIG. 1B, we now use the times of flight from three different microphones that are NOT on the same line.
From the triangle ΔSOx we havecos θ=x/d1  (8)
From the triangle ΔSOa we havecos θ=(d12−d22+a2)/2*a*d1  (9)
Set equation (8) equal to equation (9) and solve for xx=(d12−d22+a2)/2*a  (10)
Now set equation (8) equal to equation (9) and solve for zz=(d12−d32+b2)/2*b  11)
From triangle ΔSFO the y can calculated byy=sqrt(d12−x2−z2)  (12)
While the conventional system has been adequate for many years, there is a desire to develop a new system that improves customer experience, accuracy, field maintenance and cost.
Typical conventional systems utilize a measuring beam of, for example, 3.6 meters in length and 60 lbs in weight that requires two technicians to handle. A beam height of 180 mm also makes it sometimes challenging to setup for low-profile vehicles. An overall lighter, shorter, and lower-profiled beam is desirable to simplify the setup process and also improve efficiency.
In the conventional system, the precise location of each microphone must be known in order to calculate the source position. More specifically, the precise point at which the acoustic energy is detected within the microphone must be known. The microphones are assembled within and along the monolithic 3.6 meter beam. In manufacturing, a complex factory calibration system is used to accurately locate the position at which the acoustic energy is received within each microphone. Once the beam has been calibrated, a microphone or other critical electronic component in the beam must not be replaced; otherwise the beam must be once again calibrated on the factory calibration system. This limits the possibility of servicing of the beam once placed at a customer's location.
The working environment of collision repair shops is generally noisy as frame straightening, metal forming and cutting processes require extensive usage of high power hydraulic and pneumatic tools. Some of these tools along with leaking air pipes may emit acoustic energy at frequencies that disrupt normal operation of the prior art systems. Air turbulence and dramatic temperature gradient changes may also alter the quality of the air media thus interfering with the propagation of the acoustic energy from the probes.
The time of flight of the acoustic energy is affected by many characteristics of the environment such as air temperature, air pressure (or altitude) and air velocity or air currents. In addition, acoustic energy can be refracted or bent by propagating across boundaries between areas of different air density sometimes caused by local variances of these characteristics. Refraction forces the energy to travel in a curves or non-straight lines making the path longer between the source and one or more of the microphones. Refraction can cause minor to significant errors in the measured time of flight and thus the calculated position of the source.
In conventional systems, strong acoustic energy or noise from other sources, i.e., impact drills, air powered chisels, and leaking air pipes, in the surrounding area can superimpose with the acoustic energy from the probe source making it difficult to detect the short burst of energy from the spark. Noise can cause the time of flight of the source energy pulse to be measured incorrectly or missed completely.
The vehicle under repair is normally parked on the frame straightening bench, and anchored to the bench by pinchweld clamps and/or multiple steel chains or cables. Often it is also hooked to the hydraulic pulling towers to be straightened. These clamps, chains, and cables may block or alter the path of acoustic energy from probes' straight line propagation.
Over the past 15 years, passenger vehicles and the vehicle repair industry have evolved to present new requirements and challenges to a good automotive repair instrumentation system. Some extended bed pickup trucks now can be 6 meters or longer. Upper body structures of the vehicles are more and more of repair interests. Both opportunities also introduce more points of interests to be surveyed. An improved system with multiple beam expansion capability, upper body measuring capability, and the capability to support a larger number of intelligent, wireless probes is required.
In typical conventional systems, each probe is connected to the beam by a cable capable of carrying a high voltage signal to the probe electrodes for the purpose of producing a spark. This configuration has several drawbacks. A spark has a significant electro-magnetic output in addition to the acoustic output. This additional energy is subject to regulations regarding unwanted radio emissions, i.e., UL compliance. A spark requires substantial power and so requires a large power source and therefore almost certainly requires a cable. The cable connection to the beam presents inconvenience and potential hazards as cables had been reported to be accidentally cut during operations. A spark may vary its acoustic characteristics depending upon temperature, humidity, and barometric pressure. Most significant is that the voltage required for the spark to occur between the electrodes varies on these characteristics and may occur earlier or later than expected.
Further, in typical conventional systems, the measuring beam employs two identical data acquisition modules that each controls half of the microphones in the beam and up to 6 probes that are connected to its side of the beam. If the probe locates close to the mid section of the beam, the group of nearest six microphones may not be controlled by a single data acquisition module. Thus the processing of the acoustic energy from the probe must be performed by some microphones further away from the probe, compromising the accuracy of the measurement.